// postion 

.p-r{
    position: relative;
}

.p-a{
    position: absolute;
}

.p-f{
    position: fixed;
}

.p-s{
    position: static;
}

/* 绝对定位隐藏 */
.p-a-h { position: absolute; left: -999em; top: -999em; }